One of my tire pressure sensors raised a low pressure alarm on the weekend. I checked the tire pressure, and sure enough it was down but I couldn't see any visible damage or punctures. I filled the tire back up, & measured the pressure today. It seemed okay. Just as a precaution, I visited a tire store this morning and asked them to check for a leak. This is what they found;

It's a tiny staple that went right through the tire tread. I'm guessing it had been in the tire for some time, since it was such a tiny puncture and very slow leak.

It shows how important it is to frequently check your tire pressure. Thank goodness for the Tire Pressure Sensors.